As a colored metallic pigment having metallic effect excellent in Aesthetic effect, a pigment obtained by bonding a colored pigment to a metallic pigment is known in general. In this colored metallic pigment, an organic pigment such as a diketopyrrolopyrrole-based, quinacridone-based, dioxazine-based, isoindolinone-based, condensed azo-based, threne-based, perynone-based, perylene-based, phthalone-based or phthalocyanine-based pigment or an inorganic pigment such as iron oxide or carbon black is used as the colored pigment bonded to the metallic pigment.
In the aforementioned colored metallic pigment, however, the colored pigment bonded to the surface is disadvantageously easily photo-deteriorated due to optical reflection on the surface of the metallic pigment. In order to solve this problem, a pigment such as phthalocyanine blue, phthalocyanine green or iron oxide having relatively excellent light resistance must be selected, and the Aesthetic effect of the obtained colored metallic pigment is limited in the present circumstances.
In relation to a pearly pigment such as mica, on the other hand, a pigment supplied with interference colors by forming a film of silicon oxide, titanium oxide or metal on the surface is well known. However, the hiding power of such a pearly pigment is so small that an underlayer cannot be sufficiently covered even if the same is blended into paint or ink. While a metallic pigment covered with an interference film of silicon oxide, aluminum oxide or titanium oxide to be colored is disclosed as a metallic pigment having high hiding power in order to avoid this disadvantage, none is sufficient as the solving means.
Each of Japanese Patent Laying-Open No. 1-110568 (Patent Document 1) and Japanese Patent Laying-Open No. 2-669 (Patent Document 2) discloses a method of depositing titanium oxide on the surface of a metallic pigment by a sol-gel process. According to this method, however, no metallic pigment having high chroma can be obtained, and the titanium oxide layer may form a highly active anatase phase, to prompt degradation of resin and reduce weather resistance when blended into paint or the like.
Each of Japanese Patent Laying-Open No. 56-120771 (Patent Document 3), Japanese Patent Laying-Open No. 1-311176 (Patent Document 4) and Japanese Patent Laying-Open No. 6-32994 (Patent Document 5) discloses a method of forming a composite phase of iron oxide, titanium oxide and a metallic oxide and carbon, metal and a metallic oxide on the surface of a metallic pigment by a vapor phase process. When the vapor phase process is employed, however, the metallic pigment must be fluidized for supplying a precursor of the metallic oxide and heat-depositing the same on the surface of the metallic pigment. This deposition requires a specific apparatus and is extremely in danger of dust explosion of the metallic pigment, and the precursor of the metallic oxide is generally hard to handle due to strong toxicity.
Japanese Patent Laying-Open No. 8-209024 (Patent Document 6) discloses a multicoated metallic pigment based on a two-layer structure of a colorless coating layer having a refractive index of not more than 1.8 and a selective absorption layer having a refractive index of at least 2.0. Japanese Patent Laying-Open No. 8-209024 (Patent Document 6) also discloses a method of forming a metallic oxide layer on the surface of the metallic pigment by CVD (chemical vapor deposition) or by hydrolyzing a metallic compound in a solution. However, CVD has the aforementioned disadvantage. In the method of forming the metallic oxide layer by hydrolyzing the metallic compound in the solution, hydrolytic reaction is performed in a basic or acidic atmosphere containing a large quantity of water, and hence the metallic pigment reacts with water in the treatment step to result in a problem such as aggregation of the metallic pigment or runaway of the reaction.
Japanese Patent Laying-Open No. 7-258579 (Patent Document 7) discloses a luster pigment prepared by coating a substrate of aluminum flakes or the like with a multilayer film formed by a first layer consisting of silicon oxide, a silicon oxide hydrate, aluminum oxide and an aluminum oxide hydrate, a second layer consisting of metal and/or a nonselective absorption type metallic oxide and a third layer consisting of a colorless or selective absorption type metallic oxide at desire.
In the method disclosed in Japanese Patent Laying-Open No. 7-258579 (Patent Document 7), however, the thickness of the first layer tends to be nonuniform, and excellent chroma cannot be obtained. Further, the metallic oxides are not deposited on the surface of a substrate but tend to be liberated when the first layer is formed, reflected light is scattered by the liberated metallic oxide particles, and excellent metallic luster cannot be obtained. Further, while CVD and electroless plating are disclosed as methods of forming a metal layer on the first layer, CVD is dangerous and it is so difficult to homogeneously deposit the metal layer that particles not bonded with the metal are generally formed. Also in electroless plating, it is so difficult to finely and homogeneously deposit the metal layer that the metal layer is heterogeneously deposited in a scattered manner, and hence no preferable chroma can be obtained.
Japanese Patent Laying-Open No. 2003-49093 (Patent Document 8) discloses a multilayer luster pigment including a metallic base and a plurality of layers each completely enclosing the base, including at least one layer pack consisting of a colorless dielectric layer of a material having a refractive index of not more than 1.8 and another colorless dielectric layer of a material having a refractive index exceeding 1.8 and a selective or nonselective absorption layer. Japanese Patent Laying-Open No. 2003-131029 (Patent Document 9) discloses an optical multilayer system including a metal layer and a plurality of layers applied to both sides and one side thereof, including at least one layer pack consisting of a colorless dielectric layer of a material having a refractive index of not more than 1.8 and another colorless dielectric layer of a material having a refractive index exceeding 1.8 and a selective or nonselective absorption layer so that both of the layer pack and the selective or nonselective absorption layer do not completely enclose the metal layer. Japanese Patent Laying-Open No. 2003-89758 (Patent Document 10) discloses a high-saturation flaky pigment prepared by covering the overall surface of a metallic oxide-covered flaky substrate presenting interference colors due to the metallic oxide covering the same with a translucent metal thin film for strengthening the interference colors. Japanese Patent Laying-Open No. 2003-41150 (Patent Document 11) discloses a highly anticorrosive flaky metallic pigment having a coating layer comprising a metallic hydrate oxide of metal selected from a group consisting of silicon, aluminum, zirconium, titanium and tin on the surface of a flaky metallic substrate treated with a phosphoric acid compound and/or a boric acid compound. According to the method disclosed in each of Japanese Patent Laying-Open No. 2003-49093 (Patent Document 8), Japanese Patent Laying-Open No. 2003-131029 (Patent Document 9), Japanese Patent Laying-Open No. 2003-89758 (Patent Document 10) and Japanese Patent Laying-Open No. 2003-41150 (Patent Document 11), however, the degree of change of the interference colors or development of high chroma is limited, and it is disadvantageously difficult to obtain a colored metallic pigment having excellent Aesthetic effect of a satisfiable level.    Patent Document 1: Japanese Patent Laying-Open No. 1-110568    Patent Document 2: Japanese Patent Laying-Open No. 2-669    Patent Document 3: Japanese Patent Laying-Open No. 56-120771    Patent Document 4: Japanese Patent Laying-Open No. 1-311176    Patent Document 5: Japanese Patent Laying-Open No. 6-32994    Patent Document 6: Japanese Patent Laying-Open No. 8-209024    Patent Document 7: Japanese Patent Laying-Open No. 7-258579    Patent Document 8: Japanese Patent Laying-Open No. 2003-49093    Patent Document 9: Japanese Patent Laying-Open No. 2003-131029    Patent Document 10: Japanese Patent Laying-Open No. 2003-89758    Patent Document 11: Japanese Patent Laying-Open No. 2003-41150